Rotor for a synchronous rotary machine

ABSTRACT

The present invention provides a rotor for a synchronous rotary machine, having a rotor core (23) provided in its outer circumference with recesses (26), and permanent magnets (25) each fitted radially in each recess (26) so that its lower surface (25b) will be seated on the bottom surface of the recess (26). Each permanent magnet (25) and each recess (26) are formed so that gaps are formed between the inclined side surfaces (27a, 27b) of the permanent magnet (25) and the corresponding inclined side surfaces (26b, 26c) of the recess (26), and an adhesive filling up the gaps is hardened to form wedging layers (30) capable of restraining the permanent magnet (25) from being separated from the surface of the rotor core (23) by forces acting on the permanent magnet (25) to separate the permanent magnet (25) from the surface of the rotor core (23).

TECHNICAL FIELD

The present invention relates to the construction of a rotor for asynchronous rotary machine, particularly, for a synchronous electricmotor, which includes a rotor core mounted on a rotatably supportedshaft so as to serve as a yoke and having a substantially cylindricalcircumference, and permanent magnets fixedly arranged on thecircumference of the rotor core so as to interact with a rotatingmagnetic field created by a stator to thereby generate an output torque,the rotor further incorporating an improvement for preventing theseparation of the permanent magnets from the rotor core. The presentinvention also relates to a method of fabricating such a rotor.

BACKGROUND ART

Most synchronous rotary machines, particularly, synchronous electricmotors, employ either a radial magnet type rotor formed by alternatelyand contiguously arranging rotor cores serving as yokes, and permanentmagnet pieces along a circumferential direction or a surface-mountedmagnet type rotor formed by attaching a plurality of permanent magnetpieces on the outer circumference of a cylindrical rotor core.

The plurality of permanent magnets of the latter of these two types ofrotors for synchronous rotating machines, in general, are attachedadhesively with an adhesive to the substantially cylindricalcircumference of the rotor core. The adhesive strength of the adhesivemust exceed the resultant centrifugal force that acts on the permanentmagnets when the rotor rotates and the magnetic attraction resultingfrom the interactions of a rotating magnetic field created by the statorand magnetic fields created by the permanent magnets to prevent theseparation of the permanent magnets from the circumference of the rotorcore even when the rotor rotates for a long time under the action of thecentrifugal force and the magnetic attraction. Accordingly, to ensurethat the permanent magnets are securely held on the rotor, the bottomportions of the permanent magnets are partly sunk in recesses formed inthe outer circumference of the rotor core so that the permanent magnetsare held at their side surfaces by the rotor core when adhesivelyattaching the permanent magnets to the outer circumference of the rotorcore.

The prior art will be described hereunder with reference to theaccompanying drawings.

FIGS. 9A and 9B show the construction of a typical surface-mountedmagnet type rotor for a conventional synchronous electric motor, inwhich permanent magnets are held securely on the rotor core solely bythe adhesive strength of an adhesive. FIGS. 9A and 9B are a front viewand a side view, respectively, of the surface-mounted magnet type rotor.Referring to FIGS. 9A and 9B, a rotor 11 supported for rotation within astator 10 with a gap between the outer circumference thereof and thecylindrical inner circumference of the stator 10 comprises a rotor shaft12, a cylindrical rotor core 13 fixedly mounted on the rotor shaft 12, aplurality of permanent magnets 14 having the shape of a modified octagonattached by adhesive at their bottom surface to the outer circumferenceof the cylindrical rotor core 13, and end plates 15 attachedrespectively to the opposite ends of the rotor core 13 to hold the rotorcore in place on the rotor shaft 12. As mentioned above, the permanentmagnets 14 of this typical surface-mounted magnet type rotor are securedto the rotor core 13 solely by the adhesive strength of the adhesive,which is not a sufficiently effective measure to prevent the separationof the permanent magnets 14 from the rotor core 13.

FIG. 10 is a side view, corresponding to FIG. 9B, of a rotor havingpermanent magnets partly sunk in recesses formed in the outercircumference of a rotor core. As is obvious from the comparison of theconstructions shown in FIGS. 9B and 10, the construction shown in FIG.10 is more effective in preventing separation than the constructionshown in FIG. 9B. As shown in FIG. 10, a rotor core 13 is provided inits outer circumference with axial dovetail grooves 16, and permanentmagnets 14a having the shape of a curved plate and formed in a shapecomplementary to that of the dovetail grooves 16 and having an uppersurface, a lower surface of a width greater than that of the uppersurface, and side surfaces extending outward so as to approach eachother and inserted in the dovetail grooves 16. When assembling the rotorcore 13 and the permanent magnets 14a, the permanent magnets 14a neednecessarily to be inserted axially of the rotor core 13 in the dovetailgrooves 16 and positioned in place with respect to the axial direction.

Accordingly, when as shown in FIG. 11, the rotor is provided with aplurality of permanent magnets 14a divided into a plurality of groups(three groups in FIG. 11) and the groups of permanent magnets 14a arearranged respectively in a plurality of axial divisions (three axialdivisions in FIG. 11) on the outer circumference of the rotor core 13with the angular position of the permanent magnets 14a of each groupshifted relative to that of the permanent magnets 14a of other groups tosuppress torque ripple, it is impossible to insert the permanent magnets14a of the middle group axially in the corresponding dovetail grooves 16of the rotor core 13.

DISCLOSURE OF THE INVENTION

Accordingly, a principal object of the present invention is to solve theforegoing problems in the rotor of the conventional synchronous rotarymachine, particularly, in the surface-mounted magnet type rotor.

Another object of the present invention is to provide a surface-mountedmagnet type rotor comprising a rotor core, and permanent magnetsattached substantially to the outer circumference of the rotor core,capable of being assembled by assembling processes as simple as thosefor assembling the conventional surface-mounted magnet type rotorwithout requiring additional assembling work, and having a constructionhaving a mechanical fastening strength capable of securely holding thepermanent magnets on the rotor core so that the permanent magnets arenot separated from the surface of the rotor core by the centrifugalforce generated by the rotation of the rotor and the magnetic attractionresulting from the magnetic interactions of the stator magnetic fieldcreated by the stator, and the permanent magnets.

A further object of the present invention is to provide a method offabricating a surface-mounted magnet type rotor for a synchronous rotarymachine, having a rotor core provided with recesses in its outercircumference, and permanent magnets fitted in the recesses of the rotorcore by radially fitting the permanent magnets in the recesses of therotor core like tiling a surface.

In view of the foregoing object of the present invention, whenfabricating the surface-mounted magnet type rotor for a synchronousrotary machine, each permanent magnet is inserted radially in the recessformed in the substantially cylindrical surface of the rotor core. Eachrecess and each permanent magnet are formed so that wedging spaces areformed on the opposite sides of the permanent magnet between the sidefaces of the permanent magnet and walls demarcating the recess, andwedge-like layers of an adhesive are formed in the wedging spaces tosecure the permanent magnet in place against the resultant of thecentrifugal force generated by the rotation of the rotor and themagnetic attraction resulting from magnetic interactions of magneticfields created by the stator, and the permanent magnet, that tends toseparate the permanent magnet from the rotor core.

In a rotor for a synchronous rotary machine, according to the presentinvention comprising a substantially cylindrical rotor core supportedfor rotation inside a stator, and a plurality of permanent magnetsattached to the surface of the rotor core,

each permanent magnet is formed in a pieces of polygonal shape havingflat, axially opposite end faces parallel to a plane perpendicular tothe axis of rotation of the rotor, side faces each intersecting theopposite end faces, and curved upper and lower surfaces formed so as tohave curvature substantially in conformity with that of the outercircumference of the cylindrical core, the lower surface having a widthgreater than that of the upper surface so that the side faces connectingthe upper and lower surfaces are inclined so as to diverge from eachother toward the lower surface,

the cylindrical rotor core is provided in an outer surface thereof witha plurality of recesses substantially resembling a dovetail groove, eachdefined by a cylindrical bottom surface and opposite inclined side facesdiverging from each other toward the bottom of the recess so that gapsare formed between the inclined side faces of the recess and theinclined side faces of the permanent magnet when the lower portion ofthe permanent magnet is fitted radially in the recess, and arranged atfixed angular intervals, and

the gaps formed between the inclined side faces of the permanent magnetand those of the recess are filled with adhesive to form wedge-likelayer of adhesive between the inclined faces of the permanent magnet andthe inclined side faces of the recess, and the wedge-like layers ofadhesive hold the permanent magnet firmly in the recess so that thepermanent magnet will not be separated from the rotor core.

According to the present invention, a method of fabricating a rotor fora synchronous rotary machine, having a substantially cylindrical rotorcore supported for rotation inside a stator, and a plurality ofpermanent magnets adhesively attached to the cylindrical surface of therotor core comprises the steps of:

forming each permanent magnet in a piece of substantially polygonalshape having flat, axially opposite axial end faces parallel to a planeperpendicular to the axis of rotation of the rotor, inclined side faceseach intersecting the opposite end faces, curved upper and lowersurfaces having a curvature substantially in conformity with that of theouter circumference of the rotor core, the lower surface being formed soto have a width greater than that of the upper surface so that the sidefaces diverge from each other toward the lower surface;

forming a plurality of axial recesses, each having inclined side facesdiverging from each other toward the bottom of the recess so that gapsare formed between the inclined side faces of the permanent magnet andthe inclined side faces of the recess when the lower portion of thepermanent magnet is inserted radially in the recess, in the surface ofthe rotor core at fixed angular intervals;

filling the gaps formed between the inclined side faces of eachpermanent magnet and the inclined side faces of each recess withadhesive; and

hardening the adhesive filling the gaps to form wedge-like layers ofadhesive to secure the permanent magnet to the rotor core so that thepermanent magnet will not be separated from the surface of the rotorcore.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description takenin connection with the accompanying drawings, in which:

FIG. 1A is a front view of a rotor for a synchronous machine, in a firstembodiment according to the present invention;

Fig. 1B is a side view of the rotor for a synchronous machine, in thefirst embodiment according to the present invention;

FIG. 2 is an enlarged perspective view of assistance in explaining aprocedure for putting permanent magnets on a rotor core included in therotor in the first embodiment;

FIG. 3A is a fragmentary sectional view of an essential portion of therotor in the first embodiment, showing the relation between a recessformed in the rotor core, a permanent magnet and wedging layer of anadhesive on the rotor in the first embodiment;

FIG. 3B is a fragmentary sectional view of an essential portion of amodification of the rotor in the first embodiment;

FIG. 3C is a fragmentary sectional view of an essential portion ofanother modification of the rotor in the first embodiment;

FIG. 4A is a front view of a rotor for a synchronous machine, in asecond embodiment according to the present invention;

FIG. 4B is a side view of the rotor for synchronous machine, in thesecond embodiment;

FIG. 5 is an enlarged perspective view of assistance in explaining aprocedure for putting a permanent magnet on a rotor core included in therotor in the second embodiment;

FIG. 6A is a front view of a rotor for a synchronous rotating machine,in a third embodiment according to the present invention;

FIG. 6B is a side view of the rotor in the third embodiment;

FIG. 7 is an enlarged perspective view of assistance in explaining aprocedure for putting a permanent magnet of a rotor core included in therotor in the third embodiment;

FIG. 8 is a front view of a rotor in a fourth embodiment according tothe present invention;

FIG. 9A is a front view of a conventional surface-mounted magnet typefor a synchronous rotating machine;

FIG. 9B is a side view of the rotor of FIG. 9A;

FIG. 10 is a side view of another conventional surface-mounted magnettype rotor for a synchronous rotating machine; and

FIG. 11 is a front view of a third conventional surface-mounted magnettype rotor for a synchronous rotating machine.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIGS. 1A and 1B, a rotor 20 for a synchronous rotarymachine, in a first embodiment according to the present invention,similarly to the conventional rotor, is a motor element supported forrotation inside a stator 10 with a gap between the outer circumferencethereof and the cylindrical inner circumference of the stator 10. Therotor 20 comprises a rotor shaft 22, a substantially cylindrical rotorcore 23 adhesively fixed or fastened with a wedge to the rotor shaft 22,and a plurality of permanent magnets 25 fitted respectively in recesses26 formed in the outer circumference of the rotor core 23.

Each of the permanent magnets 25 is formed in the shape of a curvedpiece of plate and has a lower surface 25a curved in a curvaturecorresponding to that of the outer circumference of the rotor core 23,an upper surface having a radially outward convex shape determined onthe basis of design conditions determined taking into considerationconditions for magnetic interactions, axially opposite end faces 25cparallel to a plane perpendicular to the axis of rotation of the rotor20, and opposite, inclined side faces 27a and 27b diverging from eachother toward the lower surface 25a so as to extend opposite to the sidefaces of the recess 26 with gaps therebetween, respectively. In thisembodiment, the inclined side faces 27a and 27b extend perpendicularlyto the opposite end faces 25c.

The rotor 20, similarly to the conventional rotor, is provided with endplates 28 attached to the axially opposite ends of the rotor core 23.

In the rotor 20, each permanent magnet 25 is attached to the rotor core23 by adhesively joining the lower surface 25a thereof to the bottomsurface of the recess 26, adhesively joining the inclined side faces 27aand 27b thereof to the side faces of the recess 26 facing thereto withan adhesive and hardening the adhesive filling up gaps between theinclined side faces 27a and 27b and the side faces of the recess 26 inwedge-like layers 30 of the adhesive. Therefore, the wedge effect of thewedge-like layers 30 of adhesive holds each permanent magnet 25 securelyin a recess 26 so that each permanent magnet 25 will not be separatedfrom the rotor core 23 by the resultant of centrifugal force that actsradially outward on the permanent magnet when the rotor 20 is rotated ata high rotating speed and radial magnetic attraction resulting frominteractions of a rotating magnetic field created by the stator 10, andeach permanent magnet 25. A portion of permanent magnet 25 protrudesbeyond and outside the periphery of rotor core 23.

The recess 26 of the rotor core 23, the construction of each permanentmagnet 25, and a procedure for assembling the permanent magnet 25 andthe rotor core 23 when fabricating the rotor shown in FIGS. 1A and 1Bwill be described hereinafter with reference to FIG. 2.

Referring to FIG. 2, the plurality of recesses (eight recesses in thisembodiment) 26 are extended straight in the outer circumference of therotor core 23 along the axis of the rotor core 23 and arranged atangular intervals. Each recess 26 is a dovetail groove expandingradially inward and having a curved bottom surface 26a having the shapeof an arc of a circle, and opposite, inclined side faces 26b and 26cdiverging from each other radially inward. As mentioned above, theinclined side faces 26b and 26c are complementary respectively to theinclined side faces 27a and 27b of the permanent magnet 25, and theinclined side faces are the opposite side faces of a dovetail groovethat enables the permanent magnet 25 to be advanced radially toward thebottom surface 26a of the recess 26 of the rotor core 23 as indicated bythe arrow P in FIG. 2 when fitting the permanent magnet 25 in the recess26 and forms minute gaps between the inclined side faces 27a and 27b ofthe permanent magnet 25 and the corresponding inclined side faces 26band 26c of the recess 26 to enable the permanent magnet 25 to be removedfrom the recess 26 When the permanent magnet 25 is pulled radiallyoutward in a direction opposite the direction of the arrow P. Whenfitting the permanent magnet 25 in the recess 26, the lower surface 25aand the inclined side faces 27a and 27b thereof are coated with anadhesive. When the permanent magnet 25 is seated on the bottom surface26a of the recess 26, the minute gaps are substantially fully filled upwith the adhesive. The adhesive filling the minute gaps is hardened toform the wedge-like layers 30.

As shown in FIG. 3A, since the minute gaps between the inclined sidefaces 27a and 27b of the permanent magnet 25 and the correspondinginclined side faces 26b and 26c of the recess 26 of the rotor core 23are filled up respectively with the wedge-like layers 30 of the hardenedadhesive, the strong, mechanical wedging effects of the wedge-likelayers 30 make impossible the removal of the permanent magnet 25 fromthe recess 26 even if a force tending to separate the permanent magnet25 from the rotor core 23 acts in the direction of the arrow R oppositethe direction of the arrow P, unless the wedge-like layers 30 arecrushed. It is preferable to design the dimensional relation between thepermanent magnet 25 and the recess 26 so that the distance between theedges A along which the inclined side faces 27a and 27b of the permanentmagnet 25 intersect the lower surface 25a of the same, respectively, isslightly smaller than the distance between the edges B of the recess 26,and the edges A of the permanent magnet 25 graze the edges B of therecess 26 when the wedge-like layers 30 are not formed and permanentmagnet 25 is pulled in the direction of the arrow R. When the permanentmagnet 25 and the recess 26 are formed so as to meet such a dimensionalrelation, the wedge-like layers 30 exert the wedging effect on thepermanent magnet 25 even if a large separating force resulting from thecentrifugal force generated by the rotation of the rotor and themagnetic attraction acts on the permanent magnet and a large compressiveforce acts accordingly on the wedge-like layers 30 of adhesive, unlessthe wedge-like layers 30 are crushed completely and pushed completelyout of the gaps. Thus, the wedging effect of the wedge-like layers 30restrains the permanent magnet from being separated from the rotor core23.

In a modification shown in FIG. 3B, the inclination of the inclined sidefaces 27a and 27b of the permanent magnet 25 and the inclination of thecorresponding inclined side faces 26b and 26c of the recess 26 of therotor core 23 are greater than those of the permanent magnet 25 and therecess 26 shown in FIG. 3A to enhance the wedging effect of thewedge-like layers 30 of the adhesive.

In another modification shown in FIG. 3C, the wedging effect of thewedge-like layers 30 of the adhesive on restraining the permanent magnet25 from being separated from the rotor core 23 is enhanced by partiallyrecessing the inclined side faces 26b and 26c of the recess 26 of therotor core 23 to increase the thickness of the wedge-like layers 30 ofthe adhesive.

FIGS. 4A and 4B show shows a rotor 20 for a synchronous rotary machine,in a second embodiment according to the present invention. The rotor 20in the second embodiment differs from the rotor 20 in the firstembodiment in that recesses 26 are formed in the circumference of arotor core 23 so as to extend at a fixed helix angle θ. However, therotor 20 in the second embodiment is similar to the rotor 20 in thefirst embodiment in that the recesses 26 are formed substantiallystraight along the axis of rotation in the outer circumference of therotor core 23, the recesses 26 are arranged at angular intervals, andthe recesses 26 have the shape of a dovetail groove expanding radiallyinward. The opposite, inclined side faces 27a and 27b of each permanentmagnet 25 to be radially fitted in the recesses 26 like tiling a surfaceare formed so as to extend at a helix angle θ. Naturally, the inclinedside faces 27a and 27b, similarly to those of the first embodiment, arecoated with an adhesive, and wedge-like layers 30 are formed to securethe permanent magnet 25 firmly in the recess 26 to restrain thepermanent magnet 25 from being separated from the rotor core 23.

In the second embodiment, as is generally known, the permanent magnets25 are arranged on the rotor core 23 in an axially skew arrangementskewing at a helix angle θ to the axis of the rotor core 23 to suppresstorque ripple attributable to slots formed in the inner circumference ofthe stator 10 to hold coils therein. In assembling this surface-mountedmagnet type rotor 20, the permanent magnets 25 can be radially fitted inthe recesses 26 like tiling a surface. The wedging layers 30 formed byfilling up the gaps between the inclined side faces of the permanentmagnets 25 and the inclined side faces of the recesses 26 and hardeningthe adhesive filling up the gaps, similarly to those of the firstembodiment, hold the permanent magnets 25 in the recesses 26 so that thepermanent magnets 25 will not be separated from the rotor core 23.

FIG. 5 is a perspective view of the rotor core 23 provided with therecesses 26 skewed at a helix angle θ to the axis of rotation of therotor core 23.

FIGS. 6A, 6B and 7 show a rotor for a synchronous rotary machine, in athird embodiment according to the present invention.

As shown in FIGS. 6A, 6B and 7, recesses 126 are formed in a pluralityof axial recess divisions (three recess divisions in this embodiment)126a to 126c of a short axial length. The recesses 126 in each of therecess divisions 126a, 126b and 126c, similarly to the recesses in thesecond embodiment, are arranged in a skew arrangement skewing at a helixangle θ to the axis of rotation of the rotor 20 and have the shape of adovetail groove. However, the phase angles of the respective recesses126 of the adjacent recess groups, i.e., the recess division 126a and126b, and the recess divisions 126b and 126c, have a fixed phase angledifference β to provide permanent magnets 125 fitted in the respectiverecesses of the recess divisions 126a, 126b and 126c, with a torqueripple suppressing effect. Naturally, as is generally known, the phaseangle difference β is determined taking into consideration the degree ofthe torque ripple included in the torque produced by the magneticinteraction of a rotating magnetic field created by the stator and thepermanent magnets 125.

As shown in FIG. 7, when assembling the permanent magnets 125 and therotor core 23, the permanent magnets 125 can be radially fitted in therecesses 126 of the recess divisions 126a, 126b and 126c like tiling asurface. Accordingly, the permanent magnets 125 can be radially fittedin the recesses 126 of the recess divisions 126a, 126b and 126c in thedirection of the arrow P like tiling a surface even though the phases ofthe respective recesses 126 of the adjacent recess 126a, 126b and 126care shifted relative to each other by the phase angle difference β,which is impossible in assembling the conventional rotor in which thepermanent magnets are inserted axially in the recesses.

Naturally, the adhesive filling up gaps between the inclined side faces127a and 127b of each permanent magnet 125 and the correspondinginclined side faces 128a and 128b of each of the recesses 126 of therecess divisions 126a to 126c forms wedge-like layers 130 (FIG. 6A) whenhardened, and the strong wedging function of the wedge-like layers 130restrains the permanent magnets 125 from being separated from the rotorcore 23 by the centrifugal force generated by the rotation of the rotor20 and the magnetic attraction.

The effect of the arrangement of the permanent magnets 125 in the thirdembodiment, in which the phase of the recesses 126 of each of the recessdivisions 126a, 126b and 126c are shifted by the phase angle differenceβ relative to that of the recesses 126 of the adjacent recess divisions,on the suppression of torque ripple can be produced, for example, bydividing the axial recesses 26 of the rotor core 23 in the firstembodiment into sectional axial recesses, dividing the sectional axialrecesses into a plurality of axial recess divisions and shifting thephase of the sectional axial recesses of each of the plurality of axialrecess divisions relative to that of the sectional axial recesses of theadjacent axial recess divisions by a phase angle difference γ. A rotorprovided with permanent magnets arranged in such an arrangement is shownin FIG. 8.

In an embodiment shown in FIG. 8, axial recesses 26 are divided intosectional axial recesses of the three axial recess divisions, and thephase of the sectional axial recesses of each axial recess division isshifted by a phase angle difference γ relative to that of the sectionalaxial recess of the adjacent axial recess divisions. Although thesectional axial recesses 26 are shifted relative to each other withrespect to the circumferential direction, naturally, the permanentmagnets 25 can be radially fitted in the sectional axial recesses 26like tiling a surface similarly to those of the foregoing embodiments.

The permanent magnets employed in the foregoing embodiments havequadrilateral shapes, respectively, in a plan view. It will be easilyunderstood by a person with ordinary skill in the art to which thepresent invention pertains that the permanent magnets may be of anysuitable polygonal shape, such as the octagonal permanent magnetsemployed in the conventional rotor for a synchronous motor, providedthat each permanent magnet has side surfaces that are able to formspaces for forming wedge-like layers therein by filling up the spaceswith an adhesive and hardening the adhesive filling up the spacestogether with the corresponding side faces of a recess when thepermanent magnet is fitted radially in the recess like tiling a surface.Accordingly, permanent magnets applicable to the rotor of the presentinvention are not limited to the foregoing quadrilateral permanentmagnets.

As is apparent from the description of the foregoing embodiments,according to the present invention, a rotor for a synchronous rotarymachine, particularly, a surface-mounted magnet type rotor comprising asubstantially cylindrical rotor core and permanent magnets attached tothe outer circumference of the rotor core, has a construction thatenables the assembly of the rotor core and the permanent magnets byradially fitting the permanent magnets in recesses resembling a dovetailgroove like tiling a surface, and wedge-like layers of adhesive formedby filling up spaces formed between the side faces of the permanentmagnet and the corresponding side faces of the recess and hardening theadhesive filling up the spaces, restrains the permanent magnets frombeing separated from the rotor core by the centrifugal force generatedby the rotation of the rotor and the magnetic attraction, highlyeffectively. Thus, the construction of the rotor of the presentinvention enhances the mechanical permanent magnet anchoring forceagainst the force tending to separate the surface-mounted permanentmagnets from the rotor core remarkably and the life and reliability ofthe synchronous rotary machine incorporating the rotor of the presentinvention are improved accordingly.

Furthermore, even if the permanent magnets of the rotor are arranged ina skew arrangement or in an offset arrangement, in which the phase ofthe permanent magnets fitted in the recesses of one of a plurality ofrecess divisions is shifted relative to that of the permanent magnetsfitted in the recesses of the adjacent recess divisions, on the outercircumference of the rotor core of the rotor, the permanent magnets canbe attached to the outer circumference of the rotor core by radiallyfitting the permanent magnets in the recesses when assembling the rotor.Thus, the rotor of the present invention can be assembled by a rotorassembling method that does not require any work in addition to thatrequired by the rotor assembling method for assembling the conventionalsurface-mounted magnet type rotor and is rather simpler than the rotorassembling method for assembling the conventional surface-mounted magnettype rotor.

Although the invention has been described in its preferred forms, itwill be understood by a person with ordinary skill in the art to whichthe present invention pertains that various modifications and variationwill occur without departing from the scope of technical concept of thepresent invention.

We claim:
 1. A rotor for a synchronous rotary machine, supported for arotation inside a stator and provided with a substantially cylindricalrotor core having an outer circumference thereof to which a plurality ofpermanent magnet pieces are fixedly attached, wherein:each of saidpermanent magnet pieces comprising a polygonal shape piece having flat,axially opposite end faces parallel to a plane perpendicular to an axisof rotation of said rotor, side faces each intersecting the opposite endfaces, curved upper and lower surfaces formed so as to have a curvaturesubstantially in conformity with that of said outer circumference ofsaid cylindrical rotor core, said lower surface having a width greaterthan that of said upper surface so that said side faces connecting saidupper and lower surfaces are inclined so as to diverge from each othertoward said lower surface; said cylindrical rotor core is provided witha surface thereof formed with a plurality of substantiallydovetail-groove-like recesses each having an axially and cylindricallyextending bottom surface and opposite inclined side faces diverging fromeach other toward said bottom surface so that gaps are formed betweensaid inclined side faces of each recess and said inclined side faces ofsaid plurality of permanent magnet pieces when said lower surface ofeach of said permanent magnet pieces is radially fitted in acorresponding recess, such that a portion of said permanent magnetpieces protrude beyond an outer periphery of said rotor core, saidplurality of dovetail-groove-like recesses being circumferentiallyarranged at predetermined angular intervals; said gaps formed betweensaid inclined side faces of each of said permanent magnet pieces andsaid inclined side faces of said each recess are supplied with adhesivematerial to form wedge-like layers of said adhesive material betweensaid inclined side faces of said permanent magnet pieces and saidinclined side faces of each recess, said wedge-like layers of saidadhesive firmly holding each permanent magnet piece in correspondingrecesses to thereby prevent said permanent magnet pieces from beingseparated from said rotor core, and wherein each of saiddovetail-groove-like recesses of said rotor core is a straight grooveextending at a diagonal angle with respect to the axis of rotation ofsaid rotor, and wherein a plurality of said permanent magnet pieces aredisposed in said each diagonally extending straight groove.
 2. A rotorfor a synchronous rotary machine, supported for a rotation inside astator and provided with a substantially cylindrical rotor core havingan outer circumference thereof to which a plurality of permanent magnetpieces are fixedly attached, wherein:each of said permanent magnetpieces comprising a polygonal shape piece having flat, axially Oppositeend faces parallel to a plane perpendicular to an axis of rotation ofsaid rotor, side faces each intersecting the opposite end faces, curvedupper and lower surfaces formed so as to have a curvature substantiallyin conformity with that of said outer circumference of said cylindricalrotor core, said lower surface having a width greater than that of saidupper surface so that said side faces connecting said upper and lowersurfaces are inclined so as to diverge from each other toward said lowersurface; said cylindrical rotor core is provided with a surface thereofformed with a plurality of substantially dovetail-groove-like recesseseach having an axially and cylindrically extending bottom surface andopposite inclined side faces diverging from each other toward saidbottom surface so that gaps are formed between said inclined side facesof each recess and said inclined side faces of said plurality ofpermanent magnet pieces when said lower surface of each of saidpermanent magnet pieces is radially fitted in a corresponding recess,such that a portion of said permanent magnet pieces protrude beyond anouter periphery of said rotor core, said plurality ofdovetail-groove-like recesses being circumferentially arranged atpredetermined angular intervals; said gaps formed between said inclinedside faces of each of said permanent magnet pieces and said inclinedside faces of said each recess are supplied with adhesive material toform wedge-like layers of said adhesive material between said inclinedside faces of said permanent magnet pieces and said inclined side facesof each recess, said wedge-like layers of said adhesive firmly holdingeach permanent magnet piece in corresponding recesses to thereby preventsaid permanent magnet pieces from being separated from said rotor core,wherein each of said plurality of dovetail-groove-like recesses of saidrotor core includes a plurality of divided straight recesses, eachhaving a predetermined length extending at a predetermined diagonalangle with respect to the axis of rotation of said rotor, said pluralityof divided straight recesses being circumferentially shifted relative toeach other by a predetermined angle, and wherein a plurality of saidpermanent magnet pieces are disposed respectively in said plurality ofdivided straight recesses of each said dovetail-groove-like recess.
 3. Arotor for a synchronous rotary machine, supported for a rotation insidea stator and provided with a substantially cylindrical rotor core havingan outer circumference thereof to which a plurality of permanent magnetpieces are fixedly attached, wherein:each of said permanent magnetpieces comprising a polygonal shape piece having flat, axially oppositeend faces parallel to a plane perpendicular to an axis of rotation ofsaid rotor, side faces each intersecting the opposite end faces, curvedupper and lower surfaces formed so as to have a curvature substantiallyin conformity with that of said outer circumference of said cylindricalrotor core, said lower surface having a width greater than that of saidupper surface so that said side faces connecting said upper and lowersurfaces are inclined so as to diverge from each other toward said lowersurface; said cylindrical rotor core is provided with a surface thereofformed with a plurality of substantially dovetail-groove-like recesseseach having an axially and cylindrically extending bottom surface andopposite inclined side faces diverging from each other toward saidbottom surface so that gaps are formed between said inclined side facesof each recess and said inclined side faces of said plurality ofpermanent magnet pieces when said lower surface of each of saidpermanent magnet pieces is radially fitted in a corresponding recess,such that a portion of said permanent magnet pieces protrude beyond anouter periphery of said rotor core, said plurality ofdovetail-groove-like recesses being circumferentially arranged atpredetermined angular intervals; said gaps formed between said inclinedside faces of each of said permanent magnet pieces and said inclinedside faces of said each recess are supplied with adhesive material toform wedge-like layers of said adhesive material between said inclinedside faces of said permanent magnet pieces and said inclined side facesof each recess, said wedge-like layers of said adhesive firmly holdingeach permanent magnet piece in corresponding recesses to thereby preventsaid permanent magnet pieces from being separated from said rotor core,wherein each of said plurality of dovetail-groove-like recesses of saidrotor core includes a plurality of divided straight recesses having apredetermined length extending in parallel to the axis of rotation ofsaid rotor, said plurality of divided straight recesses beingcircumferentially shifted relative to each other by a predeterminedangle, and wherein a plurality of the permanent magnet pieces aredisposed respectively in said plurality of divided straight recesses ofeach said dovetail-groove-like recess.
 4. A method of fabricating arotor for a synchronous rotary machine, rotatably arranged inside astator and provided with a substantially cylindrical rotor core havingan outer circumference thereof to which a plurality of permanent magnetpieces are fixedly attached, said method comprising the steps of:formingeach of said permanent magnet pieces in a substantially polygonal platehaving flat, axially opposite end faces parallel to a planeperpendicular to an axis of rotation of said rotor, side faces eachintersecting said opposite end faces, curved upper and lower surfaceshaving a curvature substantially in conformity with that of said outercircumference of said cylindrical rotor core, each of said lowersurfaces being formed to have a width greater than each of said uppersurfaces, wherein side faces connecting an upper and a lower surface isinclined so as to diverge from each other toward said lower surface;forming a plurality of dovetail-groove-like axial recesses in said outercircumference of said rotor core at a predetermined circumferentialangular interval, each of said dovetail-groove-like axial recessescomprising a straight groove extending at a diagonal angle with respectto the axis of rotation of said rotor and having a cylindrical bottomsurface and opposite inclined side surfaces diverging from each othertoward said bottom surface so as to provide gaps between said inclinedside surfaces of said recess and corresponding inclined side faces ofeach permanent magnet piece when a permanent magnet piece is disposed ina corresponding recess in such a manner that a lower surface thereof isradially fitted in said recess from outside, and such that a portion ofsaid permanent magnet piece protrudes beyond said rotor core; injectingadhesive into said gaps formed between said inclined side surfaces ofeach recess and said corresponding inclined side faces of said permanentmagnet piece after radially fitting said permanent magnet piece in saidrecess of said rotor core to fill said gaps with said adhesive; andhardening said adhesive filling said gaps to form wedge-like layerscapable of restraining said each permanent magnet piece from beingseparated from said outer circumference of said rotor core.
 5. A methodof fabricating a rotor for a synchronous rotary machine, according toclaim 6, wherein said lower surface of each permanent magnet piece iscoated with adhesive to form a film-like layer of adhesive between saidlower surface of said each permanent magnet piece and said bottomsurface of said recess of said rotor core, and said film like layer ofadhesive is hardened to form a hard adhesive layer between said lowersurface of said each permanent magnet piece and said bottom surface ofsaid recess.
 6. A method of fabricating a rotor for a synchronous rotarymachine, rotatably arranged inside a stator and provided with asubstantially cylindrical rotor core having an outer circumferencethereof to which a plurality of permanent magnet pieces are fixedlyattached, said method comprising the steps of:forming each of saidpermanent magnet pieces in a substantially polygonal plate having flat,axially opposite end faces parallel to a plane perpendicular to an axisof rotation of said rotor, side faces each intersecting said oppositeend faces, curved upper and lower surfaces having a curvaturesubstantially in conformity with that of said outer circumference ofsaid cylindrical rotor core, each of said lower surfaces being formed tohave a width greater than each of said upper surfaces, wherein sidefaces connecting an upper and a lower surface is inclined so as todiverge from each other toward said lower surface; forming a pluralityof dovetail-groove-like axial recesses in said outer circumference ofsaid rotor core at a predetermined circumferential angular interval,each of said dovetail-groove-like axial recesses of said rotor coreincluding a plurality of divided straight recesses, each having apredetermined length extending at a predetermined diagonal angle withrespect to the axis of rotation of said rotor, said plurality of dividedstraight recesses being circumferentially shifted relative to each otherby a predetermined angle, each of said plurality of divided straightrecesses having a cylindrical bottom surface and opposite inclined sidesurfaces diverging from each other toward said bottom surface so as toprovide gaps between said inclined side surfaces of said recess andcorresponding inclined side faces of each permanent magnet piece when apermanent magnet piece is disposed in a corresponding recess in such amanner that a lower surface thereof is radially fitted in said recessfrom outside, and such that a portion of said permanent magnet pieceprotrudes beyond said rotor core; injecting adhesive into said gapsformed between said inclined side surfaces of each recess and saidcorresponding inclined side faces of said permanent magnet piece afterradially fitting said permanent magnet piece in said recess of saidrotor core to fill said gaps with said adhesive; and hardening saidadhesive filling said gaps to form wedge-like layers capable ofrestraining said each permanent magnet piece from being separated fromsaid outer circumference of said rotor core.
 7. A method of fabricatinga rotor for a synchronous rotary machine, rotatably arranged inside astator and provided with a substantially cylindrical rotor core havingan outer circumference thereof to which a plurality of permanent magnetpieces are fixedly attached, said method comprising the steps of:formingeach of said permanent magnet pieces in a substantially polygonal platehaving flat, axially opposite end faces parallel to a planeperpendicular to an axis of rotation of said rotor, side faces eachintersecting said opposite end faces, curved upper and lower surfaceshaving a curvature substantially in conformity with that of said outercircumference of said cylindrical rotor core, each of said lowersurfaces being formed to have a width greater than each of said uppersurfaces, wherein side faces connecting an upper and a lower surface isinclined so as to diverge from each other toward said lower surface;forming a plurality of dovetail-groove-like axial recesses in said outercircumference of said rotor core at a predetermined circumferentialangular interval, each of said dovetail-groove-like axial recesses ofsaid rotor core including a plurality of divided straight recesseshaving a predetermined length extending in parallel to the axis ofrotation of the rotor, said plurality of divided straight recesses beingcircumferentially shifted relative to each other by a predeterminedangle, each of said recesses having a cylindrical bottom surface andopposite inclined side surfaces diverging from each other toward saidbottom surface so as to provide gaps between said inclined side surfacesof said recess and corresponding inclined side faces of each permanentmagnet piece when a permanent magnet piece is disposed in acorresponding recess in such a manner that a lower surface thereof isradially fitted in said recess from outside, and such that a portion ofsaid permanent magnet piece protrudes beyond an outer periphery of saidrotor core; injecting adhesive into said gaps formed between saidinclined side surfaces of each recess and said corresponding inclinedside faces of said permanent magnet piece after radially fitting saidpermanent magnet piece in said recess of said rotor core to fill saidgaps with said adhesive; and hardening said adhesive filling said gapsto form wedge-like layers capable of restraining said each permanentmagnet piece from being separated from said outer circumference of saidrotor core.